Dear Number Two,

I know you might have sex with her, and that really isn't a problem. What is a problem is that you might have sex with her without a condom, which means you and I can't have sex anymore, since I don't want to use a condom when I have sex with you. Period. So please, if you find yourself preparing to do anything involving penetration with her tonight, or any night with anyone for that matter, please use a condom with them, so you don't have to use a condom with me.

In words that might mean more to you, if you have to use a condom when you and I have sex, you're gonna have to live without the oral break between positions, because seriosuly, have you ever tasted latex? Gross.

(By the way, I know that second paragraph sounds like I might be willing to try intercourse with you without a condom, but if it's not great in other ways, I'm really, really gonna miss you)